1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine, a printer, a facsimile telegraph, etc.
2. Related Background Art
For example, the construction of an image forming apparatus using an intermediate transfer member is adopted in an image forming apparatus having a full color or multiplex image forming function in many cases.
In this image forming apparatus, component color toner images corresponding to plural color component images of a full color image or a multiplex image as an object are sequentially formed on a first image bearing member such as an electrophotographic photosensitive member, an electrostatic recording dielectric, etc. by suitable image forming process means. These component color toner images are sequentially superimposed and transferred to the intermediate transfer member as a second image bearing member being generally of a rotary belt type by a primary transfer portion. Thus, a full color image and a multiplex toner image corresponding to the full color image and the multiplex image as an object are synthesized and formed on the intermediate transfer member. The toner image synthesized and formed on this intermediate transfer member is transferred to a transfer material by a secondary transfer portion. This transfer material is guided to a fixing portion and the image is fixed so that a full color image forming object is obtained.
Here, the image forming apparatus adopting an intermediate transfer belt as the second image bearing member (intermediate transfer member) will be explained with reference to FIG. 11. FIG. 11 shows the image forming apparatus with an intermediate transfer unit 120 and a cleaner unit 112 as centers, and shows only one of plural image forming portions.
Component color toner images corresponding to plural color component images formed on an image bearing member 101 are sequentially superimposed and transferred by a primary transfer portion T1 nipped between the image bearing member 101 and a primary transfer opposite roller 102. Thus, a full color image as an object is formed on an intermediate transfer belt 103. This full color image on the intermediate transfer belt 103 is collectively transferred to a transfer material P by a secondary transfer portion T2 formed by a secondary transfer roller 118 and a secondary transfer opposite roller 105. The full color image is then fixed by an unillustrated fixing portion so that a full color forming object is obtained.
The intermediate transfer unit 120 is composed of the primary transfer opposite roller 102, the intermediate transfer belt 103, rollers of three shafts for supporting the intermediate transfer belt 103, i.e., a drive roller 104, the secondary transfer opposite roller 105, and a tension roller 106 as a movable roller. The intermediate transfer unit 120 can be detachably attached to an apparatus main body.
Tensile force of the intermediate transfer belt 103 is constantly maintained by pressurizing a bearing 107 of the swingable tension roller 106 by a compressing spring 108.
The cleaner unit 112 is arranged around the intermediate transfer belt 103 and cleans toner not transferred in the secondary transfer but left as the residual transfer remaining on the intermediate transfer belt 103. The cleaner unit 112 has a cleaning blade 111 abutting on the intermediate transfer belt 103, and a cleaner container 110 for containing the remaining toner removed by the cleaning blade 111. The cleaning blade 111 is retained by the cleaner container 110. A backup roller 109 is arranged in an opposite portion of the cleaning blade 111. The cleaner unit 112 and the backup roller 109 are fixed to the apparatus main body or the intermediate transfer unit 120.
Japanese Patent Application Laid-open No. 5-289426 discloses a cleaning blade arranged such that the cleaning blade is opposed to a tension roller for tensioning a photosensitive belt. A photosensitive member unit having first and second casing members is disclosed more particularly. A shaft of a drive roller for driving the photosensitive belt and a shaft of an exposure roller for supporting an exposure position of the photosensitive belt are assembled into the first casing member. A charger for charging the photosensitive belt and a cleaning blade for cleaning the photosensitive belt are assembled into the second casing member.
Further, it is also disclosed that a shaft of the tension roller is guided to an elongated hole formed in the first casing member and is also guided to an elongated hole formed in the second casing member.
However, the following problems exist in the above conventional example since the cleaner unit 112 of the intermediate transfer belt 103 is fixed to the main body or the intermediate transfer unit 120.
(1) The tension roller 106 for maintaining the tensile force of the intermediate transfer belt 103 constant and a roller for controlling the deviation of the belt are movable to make an alignment adjustment. Therefore, the position of a surface of the intermediate transfer belt 103 is also changed in accordance with the positions of the movable rollers. In such a case, the cleaning blade 111 does not abut against the intermediate transfer belt 103 depending on the position of the surface of the intermediate transfer belt 103, and hence the cleaning blade 111 does not fulfil its role as a cleaner. Further, the backup roller 109 is required in the opposite portion of the cleaning blade 111 so that the number of parts is increased and the construction becomes complicated.
(2) When the cleaner unit 112 is fixed to the intermediate transfer unit 120 and when one of the intermediate transfer belt 103 and the cleaner unit 112 is exchanged by life, etc., both the units must be simultaneously exchanged, which is not economical and efficient.
In the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 5-289426, the tension roller is displaced in two directions and these two directions are not perpendicular to each other at any time. Accordingly, when the tension roller is displaced, abutting positions of the tension roller and a tip of the cleaning blade abutting through the photosensitive belt are changed. Namely, an abutting angle of the cleaning blade on the photosensitive belt and an inroad amount of the cleaning blade tip are changed. Therefore, there is a fear of generation of a cleaning defect in which toner passes through the cleaning blade, etc.
An object of the present invention is to provide an image forming apparatus for preferably maintaining a contact state of a cleaning member and a belt member and able to prevent the generation of a cleaning defect even when a roller for supporting the belt member is moved.
The other objects of the present invention will become apparent by reading the following detailed explanation.